حسین نجات بخش

Orthotropic plates used in composite structures are subject to local buckling, including compressive buckling. In the process of designing and building most large structures or instruments with complex geometry, joints in the structure are unavoidable. Today, adhesive joints are widely used in connecting composite structures due to some advantages over mechanical joints. In this article, the buckling phenomenon of orthotropic rectangular multilayer plates connected with glue has been investigated, and the force effects of the glue layer under buckling loading conditions have been studied. In order to obtain the critical buckling loads under different boundary conditions, the generalized differential quadrature method (GDQM) has been used. Buckling analysis is presented based on first-order shear deformation theory (FSDT) for carbon/epoxy, glass/epoxy and Kevlar/epoxy composite materials with different porcelain layers. The effect of thickness and type of the adhesive as a bonding layer has been investigated. In plates made of a type of porcelain layer, two-way carbon epoxy plates show higher buckling strength, and in general, the higher the ratio of length to width of the plates is, the higher the buckling strength will be. In the connections, the obtained results have been compared with the results from the finite element analysis in ABAQUS commercial software.

Numerical analysis of damage of large structures in real dimensions is a complex and time-consuming analysis. Therefore, it is important to use a simple and accurate damage model. In this research, the test and numerical analysis of damage in the composite wing structure of an airplane in real scale in bending loading was done. For a more complete review of the test results, extracting more data about the way of causing damage and also estimating the strength of the structure, the wing structure including spars and ribs, as well as the effect of fabric patches in the finite element software ABAQUS was modeled and subjected to damage analysis using USDFLD subroutine. After the initiation of damage, this subroutine reduces the mechanical properties suddenly. Examining the results of numerical and experimental analysis showed that the used damage model can accurately simulate the mechanical behavior of the wing structure. From the results, it was found that the numerical model and the composite wing structure have the same stiffness; but the strength of the analyzed wing is lower than the final strength observed in the bending test. Comparing the results of the strain gauges with the results of the analysis also shows that the modeling of the structure with the  layup details is done correctly and the damage model is implemented with appropriate accuracy in the software. Therefore, it seems that, this damage model can be used for damage analysis of real and large composite structures with appropriate speed and accuracy